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Highlights • Perceptions and accepted levels of wildness in tropical urban greenery are tested. • Respondents, in principle, are not against moderately wilder urban greenery. • Utilitarian values are stronger factors of preference rather than eco-centric or aesthetic ones. • People in Singapore accept up to moderately wilder conditions for parks and low wildness for streetscapes. • More flowers, fauna, and boardwalks improve people's preference for wild landscape. Abstract Urban green spaces (UGS) have the potential to aid in the restoration of ecosystem services and biodiversity in cities, but this function is often diluted because ecological processes are ignored in favour of 'tidiness'. While the general public is not fond of unkempt greenery, a less-manicured UGS that balances the spontaneous growth of plants and maintenance regimes may be accepted. The paper describes a study exploring accepted degrees of UGS wildness, specifically areas that are currently mown lawns. In the study, a photo elicitation survey administered two sets of photos to two groups of respondents, 663 members of the general population and an additional 48 members of nature/environmental interest groups. The survey assessed perceptions of managed greenery, with three different degrees of growth of lawns in four contexts and six types of landscape elements in wilder lawns. The study found the preferred level of wildness of UGS varied depending on the context, people were generally not against moderately wilder UGS. The utilitarian aspect of landscape was a primary factor in the preference for less-manicured lawns, and aesthetics were a secondary factor. Also, general population characteristics did not consistently predict preference for any vegetation growth condition, and landscape elements differentially affected the degree of preference for wilder lawns. The article concludes by discussing the practical consequences of these findings for the inclusion of wilder UGS in design and management. [ABSTRACT FROM AUTHOR]

Leveraging the benefits offered by nature-based solutions (NBS) will be vital in addressing present and future environmental and social challenges as urban densification continues to exert pressure on cities. The greening of urban streets, in particular, provides many benefits in terms of livability, health, and biodiversity. While many studies have explored the suitability of NBS in a particular context considering the benefits they provide in relation to local environmental challenges (e.g. filtering the air in areas with high pollution, absorbing water in areas prone to flooding), this study focuses on residents' perspectives on and their demand for NBS. This is particularly relevant given the importance of public acceptance of NBS measures for their success. The research presented in this paper is based on a mixed-methods study, combining an online survey and eight focus group interviews, which aimed to better understand which types of NBS people prefer, how much and what types of street space they are willing to exchange for street greening, and the opportunities and concerns they have regarding varying degrees of street greening. Findings suggest that respondents are overwhelmingly in favor of greening their street with NBS, yet preferred NBS and opinions on where to implement them vary among participants. Further, street greening was thought to come up against other understandings of how streets should be used and for what purpose. These considerations should be taken up by planners to improve the uptake of NBS. [ABSTRACT FROM AUTHOR]

Interactions between tree roots and sidewalks can result in damage to sidewalks and when sidewalk damage is repaired adjacent tree roots are often severed. The objective of this study was to quantify the growth response of urban trees in restricted planting spaces pre- and post-sidewalk construction. The research included four trees species commonly planted along streets in Minneapolis and Saint Paul, Minnesota, USA. Species included were: Acer platanoides, Celtis occidentalis, Gleditsia triacanthos, and Tilia spp. Two street tree populations were sampled: trees adjacent to replaced sidewalk panels (<1.75 m) and trees on streets with sidewalk construction that were greater than 3 m from replaced sidewalk sections. In total, increment core samples from 292 trees were analyzed. Annual rings from each tree were measured and converted to basal area increment (BAI) for analysis. Comparisons of BAI were conducted between the two sample populations to assess differences in tree growth patterns. Pre- and post-sidewalk construction BAI was also evaluated to determine the influence of construction on growth trajectory. Growth response was quantified using resistance, resilience, and recovery indices. Species were found to differ in their response to construction disturbance. Planting space width was also found to influence post-construction growth. Tilia spp. had the highest resilience and fastest overall growth recovery post-sidewalk construction and A. platanoides exhibited the lowest resistance, resilience, and recovery post-sidewalk construction. [ABSTRACT FROM AUTHOR]

Apart from influencing the amount of leaf-deposited particles, tree crown morphology will influence the local distribution of atmospheric particles. Nevertheless, tree crowns are often represented very rudimentary in three-dimensional air quality models. Therefore, the influence of tree crown representation on the local ambient PM 10 concentration and resulting leaf-deposited PM 10 mass was evaluated, using the three-dimensional computational fluid dynamics (CFD) model ENVI-met ® and ground-based LiDAR imaging. The modelled leaf-deposited PM 10 mass was compared to gravimetric results within three different particle size fractions (0.2–3, 3–10 and >10 μm), obtained at 20 locations within the tree crown. Modelling of the LiDAR-derived tree crown resulted in altered atmospheric PM 10 concentrations in the vicinity of the tree crown. Although this model study was limited to a single tree and model configuration, our results demonstrate that improving tree crown characteristics (shape, dimensions and LAD) affects the resulting local PM 10 distribution in ENVI-met. An accurate tree crown representation seems, therefore, of great importance when aiming at modelling the local PM distribution. [ABSTRACT FROM AUTHOR]

Vegetation barriers have been widely applied along urban streets to improve roadside air quality. For a deep investigation of their influences, field measurements and numerical simulations are performed in this study. Carbon monoxide (CO) is selected as a representative of gaseous traffic emissions for both field observations and numerical models. Computational Fluid Dynamics (CFD) models of the standard k-ε turbulent model and Eulerian approach for species transport are solved by FLUENT solver. Results obtained from numerical simulations show a good agreement with field observations on the distribution of roadside CO. In perpendicular wind conditions, both field observations and numerical simulations present a prominent CO reduction over the slow lanes (footpath and bikeway) when vegetation barriers exist. To effectively mitigate roadside air pollution, numerical simulations also provide the optimal heights for roadside vegetation barriers in the given street canyons. For street canyons with an aspect ratio (the ratio of building height to street width) ranging from 0.3 to 1.67, 1.1 m can be used as an optimal height, and 2.0 m could serve as an alternative if tall vegetation barriers are considered. For street canyons with an aspect ratio of lower than 0.3, 0.9 m to 2.5 m can be considered as the optimal heights for roadside vegetation barriers. According to sensitivity analysis, the optimal heights for vegetation barriers are largely insensitive to wind velocities in the given street canyons. In the more complicated urban street canyons and complex meteorological conditions, the optimal heights can be determined by specific numerical simulations. These findings are expected to provide important insights into alleviation of gaseous mobile emissions in terms of vegetation barrier design in urban streets. [ABSTRACT FROM AUTHOR]

In 1997, Quercus bicolor and Quercus phellos in a New York City streetscape were planted in CU-Structural Soil under a concrete sidewalk and in a tree lawn with the intention of observing long term plant response as a comparative study of an early installation of the new designed soil method. The trees have been measured nine times since the second year post-installation. We present the growth of trunk diameter, height and slenderness ratios. To verify root colonization in the structural soil under the sidewalk, tree root presence was measured using ground-penetrating radar in 2009, year 12. In the 17th year, trees in the sidewalk were similar in size with a higher level of survivorship as compared to the trees in the tree lawn. Adjusting for year of replacement in the tree lawn, model predictions for diameter of trees 15 years post-installation were no different for Q. bicolor in either the sidewalk (21.38 cm) or the tree lawn (22.05 cm). Q. phellos in the tree lawn were predicted to be slightly larger, 34.29 cm versus 31.34 cm in the sidewalk. Roots had colonized the structural soil under the sidewalk to 60 cm, its full depth. This provided evidence that the structural soil medium served as an acceptable rooting environment. [ABSTRACT FROM AUTHOR]

We explored Google Street View (GSV) as a street-level, urban greenery assessment tool. Street-level greenery has long played a critical role in the visual quality of urban landscapes. This living landscape element can and should be assessed for the quality of visual impact with the GSV information, and the assessed street-level greenery information could be incorporated into urban landscape planning and management. Information on street-level views of urban greenery assessment, however, is rare or nonexistent. Planners and managers’ ability to plan and manage urban landscapes effectively and efficiently is, therefore, limited. GSV is one tool that might provide street-level, profile views of urban landscape and greenery, yet no research on GSV for urban planning seems available in literature. We modified an existing Green View Index (GVI) formula and conducted a case study assessment of street greenery using GSV images in the area of East Village, Manhattan District, New York City. We found that GSV to be well suited for assessing street-level greenery. We suggest further that the modified GVI may be a relatively objective measurement of street-level greenery, and that GSV in combination with GVI may be well suited in guiding urban landscape planning and management. [ABSTRACT FROM AUTHOR]

Knowledge of how to increase the restorative quality of residential streetscapes may help to offset problems entailed by urban densification. The present study considered the effects of trees, grass, and flower beds on ratings of restoration likelihood for streetscapes. We used digital-imaging techniques to systematically vary these natural elements in images of residential streets with different architectural characteristics. Using a web-based procedure, 103 images were rated by independent groups of Icelandic adults ( N = 188) on either restoration likelihood, preference, being away, or fascination. Group mean scores on the psychological variables were calculated for each image, and the images were then used as the units of analysis in regression analyses. Ratings of restoration likelihood increased with increase in the number of street trees and the presence of flower beds. These effects were apparently mediated by perceptions of being away and fascination. The architectural characteristics of buildings along the streets had a strong independent effect on restoration likelihood ratings, but they did not moderate the positive effects of vegetation on restoration likelihood ratings. The results provide guidance for the design of more psychologically sustainable urban residential environments. [ABSTRACT FROM AUTHOR]

Raingardens are increasingly common in sustainable stormwater management in cities around the world. Implementing raingardens will change the appearance of conventional urban streetscapes and this is especially important when retrofitting raingardens into existing streets. Raingardens need to fulfil both technical and aesthetic functions. Aesthetic function, assessed as landscape preference, must be understood to ensure that retrofitted raingardens are appropriately designed and managed. Scholars have long adopted a Likert rating scale- to determine landscape preference. Limitations of this method led market researchers to develop choice-based ranking, including best-worst scaling, to assess preference. Thus, this study uses best-worst scaling to assess landscape preference by residents for pairs of streetscapes with and without raingardens in four suburbs of Melbourne, Victoria, Australia. These preference data, and attitudes towards raingardens, stormwater harvesting and own streetscapes, inform guidelines for design and management of retrofitted raingardens. Findings revealed respondents' overwhelming support for harvesting and reuse of stormwater, though support for fit-for-purpose stormwater reuse decreased as personal proximity increased. While attitudes towards raingardens were positive and most respondents liked the raingardens in their own street, less than one-quarter helped to maintain them. Across all respondents, maintenance of raingardens in streetscapes was regarded as the responsibility of local government. Nevertheless, many would install raingardens in their own property. Overall, streetscapes with raingardens were preferred to those without. Residency in a street with or without raingardens did not influence preference, however, residency in a particular street did. Indeed, context was important: preference for one's own streetscape varied statistically significantly between residents of inner- and outer-Melbourne suburbs. Drawing on these results, four guidelines for design and management of retrofitted raingardens are proposed: 1. Understand context; 2. Consider how the street is used; 3. Select appropriate plants and planting style; 4. Ensure adequate maintenance. [ABSTRACT FROM AUTHOR]